A Moment of Science

Soap’s Magic Ingredient

Soap has a magic ingredient that helps clean clothes and dishes.

soapy bubbles

Photo: pareeerica (flickr)

Soap bubbles can form with enough soap.

Washing dishes without soap just doesn’t do the trick — especially if the dishes are greasy.

But what is it about that magic ingredient, soap, that gets clothes, dishes, and bodies cleaner than they can get with water alone?

What’s In Soap?

The soap molecule is kind of a schizophrenic molecule. It consists of a long chain of carbon atoms with one end that’s attracted to water and another end that’s repelled by water.

You can see how soap works if you put a few drops of oil in a dish of water and stir the oil into droplets with your finger; when you stop stirring, the small droplets tend to recombine into larger droplets.

In another dish, try the same thing, but this time add a few drops of dish washing liquid. As you begin to stir, you’ll notice the soap clings to the edge of the oil droplets.

Keep stirring and you’ll see the oil breaks up into much smaller droplets than in the other dish. Then you stop stirring, you’ll find the droplets do not immediately begin recombining.

Soap And Water

By clinging to the edge of the oil, the end of the soap molecule that is attracted to water can stay in the water while the end that is repelled by water can stick to the oil.

As you start stirring the oil and water, the oil drop breaks up into smaller droplets, but because those droplets immediately become surrounded by soap molecules, it becomes much harder for them to go back together again.

When you scrub a greasy pot, the physical action of your hand breaks up the grease. The soap then surrounds the grease particles, keeping them from recombining or from returning to the side of the pot.

  • http://www.facebook.com/profile.php?id=1106544151 Sara Ali Borders

    Amphipathic molecules!!

  • http://www.facebook.com/profile.php?id=1106544151 Sara Ali Borders

    Just like the cell membrane

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